The purpose of this study is to generate data on immunogenicity and safety of the monovalent H1N1 vaccine in support of the development and registration.

Inclusion Criteria:

• Male or female aged >= 6 months to =<35 months at the time of the first study vaccination. Born at full term of pregnancy (≥ 37 weeks) and with a birth weight ≥ 2.5 kg
• Informed consent form has been signed and dated by the parent(s) or other legally acceptable representative Subject and parent/legal representative are able to attend all scheduled visits and to comply with all trial procedures

Exclusion Criteria:

• Participation in another clinical trial investigating a vaccine, drug, medical device, or a medical procedure in the 4 weeks preceding the first trial vaccination
• Planned participation in another clinical trial during the present trial period
• Receipt of any vaccine in the 4 weeks preceding the first trial vaccination
• Planned receipt of any vaccine prior to the Day 42 blood sample
• Receipt of blood or blood-derived products in the past 3 months which might interfere with the assessment of immune response
• Known or suspected congenital or acquired immunodeficiency, immunosuppressive therapy such as anti-cancer chemotherapy or radiation therapy within the preceding 6 months, or long-term systemic corticosteroid therapy (prednisone or equivalent for more than 2 consecutive weeks within the past 3 months)
• Known systemic hypersensitivity to any of the vaccine components, or history of a life-threatening reaction to the vaccine(s) used in the trial or to a vaccine containing any of the same substances
• Thrombocytopenia contraindicating intramuscular (IM) vaccination as reported by parents/legal representative
• Bleeding disorder or receipt of anticoagulants in the 3 weeks preceding inclusion contraindicating IM vaccination
• Chronic illness that in the opinion of the Investigator is at a stage where it might interfere with trial conduct or completion
• Family members of the employees or the Investigator
• Previous participation in a trial investigating a vaccine with the swine-origin A/H1N1 influenza strain
• Confirmed infection with the novel influenza A/H1N1 strain
• Febrile illness (temperature ≥ 38.0°C) or moderate or severe acute illness/infection on the day of vaccination, according to Investigator judgment